When urban tunnels are driven, settlement of the daylight surface is one of the forms of deformation experienced by the soil mass. This process is investigated by the following methods. Empirical methods make it possible to describe the displacement distribution of the daylight surface of a soil mass using certain experimentally established coefficients. Gauss' curve [1], which has two important parameters (maximum surface settlement S max above the axis of the tunnel, and distance i to the inflection point of the surface-settlement curve) is used to describe the surface-settlement profile of a single-barrel tunnel. Peck's formula and several empirical formulas in which the dimensions of the settlement basin are determined primarily by the depth of embedment Z 0 of the tunnel and its diameter D alone are presented in Table 1.Basic inadequacies of the empirical methods are as follows: low accuracy; disregard of equations of state of the materials; impossibility of evaluating the displacement and stress within the soil mass; and, impossibility of compiling a prognosis for newly designed structures.Analytical methods based on positions of the theory of elasticity are presented in [2][3][4]. Sagaseta [3] has developed a solution in closed form for an isotropic uniform incompressible soil (Poisson's ratio of 0.5). Here, has considered only the radial compression of the tunnel section in an elastic half space. Verruijt and Booker [4] analyzed two forms of tunnel deformations -radial compression of the section, and variation in the shape of the tunnel in compressible elastic soils (Poisson's ratio of less than 0.5). Loganathan and Poulos [2] considered the internal friction of the rocks spanning a tunnel. Their analytical solution includes Poisson's ratio, the depth of embedment of the tunnel, and its diameter. The analytical solutions are suitable primarily for rocks. They do not allow for consideration of the conditions under which the rock occurs, the presence of water-bearing seams, the construction phases, and other factors.In contrast to the analytical solutions, numerical methods make it possible to account for a multitude of factors describing the "soil-mass/tunnel" system, including the mutual effect of several tunnels.Methods of estimating surface settlement during the driving of tunnels are described. A combination of empirical, analytical, and numerical methods makes it possible to predict the dimensions of a settlement basin. In the course of solving the inverse modeling problem, parameters of the model are established and forecasting charts of maximum surface settlement are compiled.
Subsidence of the daylight surface is one of the characteristic types of soil deformation encountered during subway tunneling. To minimize damages sustained by existing buildings and foundations on the surface of the ground, it is necessary to predict these effects.The finite-element method implemented in the PLAXIS program, which permits modeling of soil excavation for, and lining of a tunnel, was used to estimate surface subsidence [1]. Analyses were performed for the U-8-Nord subway line in Munich (Germany). Data derived from field observations of surface subsidence on completion of a section of the subway, which were acquired by coworkers of the Technical University under the guidance of I. Fillibeck, served to verify the model. Maximum surface subsidence amounted to 7 mm. Subsidence was recorded at distances of up to 10 m from the axis of the tunnel.The geologic section of Munich is represented by Quaternary gravelly-rubbly soils underlain by Tertiary sandy and clayey soils. The computational section over which the modeling was conducted comprises three lithologically different layers. The upper 10-m-thick layer consists of gravel, under which resides a layer of sand 4 m thick, and then a layer of clay 8 m thick. The physico-mechanical properties of the soils are presented in Table 1. The elastic moduli and strength indicators of the soils were determined from data derived in triaxial and compression tests. The ground-water table is located 8 m below the surface of the ground.The tunnel was opened by the shielded method in the gravel and sand layers. The 7-m-diameter tunnel was situated at a depth of 13 m. Basic properties of the tunnel lining were: normal stiffness EA = 6.0 . 10 6 kN/m; bending stiffness EI = 2.0 . 10 4 kNm 2 /m; equivalent thickness d = 0.2 m; weight w = 8.4 kN/m/m; and, Poisson's ratio v = 0.33.A 15-node element was used as the basic type of finite elements. The grid of finite elements was thicker in the zone of surface subsidence. Excavation of the soil and installation of the tunnel lining were modeled in accordance with two methods [2]: the β-method (β: 0.4, 0.5, 0.6, and 0.7%), and the Results are presented for modeling of surface subsidence resulting from boring operations for construction of the U-8-Nord subway line in Munich. Measurements of surface subsidence on completion of tunneling operations served as verification for the model. A soil-behavior model, describing most reliably the subsidence of the ground surface during tunneling was selected. Factors controlling surface subsidence were determined.
Abstract. The article presents the results of hydrogeological studies carried out within the area of the Kama river bank in Perm city. It proposes the hydrodynamic model by means of which a number of forecasting issues have been addressed. The possible scenarios of changes in filtration flow, i.e. water rise before the obstacle and water drop behind the obstacle due to groundwater filtration blockage, have been described [2]. The allowable changes of hydrodynamic conditions within the study area have been outlined.
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